U.S. Pat. No. 4,821,114 has disclosed an optical illumination system having a filter wheel and a white light source in the form of a lamp. In this case, blocking filters, such as absorption filters and dichroitic filters, for example, are used. They are inserted into the beam path of virtually point light sources such as xenon high-pressure discharge lamps. A continuous change in color is therefore only possible with a plurality of filter wheels and needs to be realized in a complex manner by mechanical means. The filter wheels are positioned one behind the other and rotated appropriately. The control is complex and the filters are very expensive.
Control for groups of LEDs is specified, for example, in U.S. Pat. Nos. 5,515,136 and 6,630,801. DE-Az 10 2005 041 319.6 has described a module in which a plurality of high-efficiency LEDs are combined on one printed circuit board. These are then imaged onto one point.
Imageable ultra-high power LEDs at present represent one of the greatest technical challenges. In addition to the production of white light, in particular the implementation of imageability plays an important role. Previous attempts have therefore proposed the superimposed imageability of a plurality of LEDs. However, this has various disadvantages. A relatively complex system which images a plurality of LEDs at the same time is cost-intensive since the optical arrangements need to be applied a plurality of times.
A quite different substantial disadvantage with the known solutions is the fact that white LEDs are used which are in the form of conversion LEDs. This means that a fluorescent layer converts the primarily emitted light from the LEDs partially or completely into longer-wave radiation. In the process, the phosphor needs to be applied in the direct vicinity of the chip. However, these phosphors are in principle more or less thermally sensitive. At junction temperatures beyond 150° C., all known phosphors display significant losses of efficiency owing to thermal quenching. Individual phosphors which are very suitable per se at room temperature are even considerably more sensitive. Overall, this results in reduced efficiency. Until now, there has been no sensible technical solution to this.